In a letter to Attorney General Eric Holder, the lawmakers said they've learned trial attorney Barbara Kay Bosserman is leading the probe. They detailed federal campaign finance records showing she's given more than $6,000 to Obama's two presidential campaigns -- and urged Holder to remove her from the case.

"By selecting a significant donor to President Obama to lead an investigation into inappropriate targeting of conservative groups, the Department has created a startling conflict of interest," Rep. Darrell Issa, R-Calif., chairman of the House Oversight and Government Reform Committee, and Rep. Jim Jordan, R-Ohio, wrote in the letter. "It is unbelievable that the Department would choose such an individual to examine the federal government's systematic targeting and harassment of organizations opposed to the President's policies. . . .